HYDROTHERMAL SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF 2 CALCIUM VANADIUM(III) PHOSPHATES - CA2V(PO4)(HPO4)2.H2O AND CA2V(PO4)(P2O7)

The new phosphate Ca2V(PO4)(HPO4)2.H2O and the dehydrated compound Ca2V(PO4)(P2O7) have been synthesized hydrothermally at 230 and 450-degrees-C, respectively, and characterized by single-crystal X-ray diffraction and thermogravimetric analysis. Crystal data: Ca2V(PO4)(HPO4)2.H2O, monoclinic, C2/c, a = 7.531 (2) angstrom, b = 15.522 (4) angstrom, c = 9.149 (2) angstrom, beta = 113.52 (2)-degrees, Z = 4, R = 0.0215 for 954 unique reflections; Ca2V(PO4)(P2O7), monoclinic, P2(1)/c, a = 6.391 (2) angstrom, b = 6.6362 (9) angstrom, c = 19.071 (2) angstrom, beta = 99.26 (2)-degrees, Z = 4, R = 0.029 for 1389 unique reflections. The structure of the hydrated compound consists of infinity 1[V(PO4)2/2(HPO4)4/2] along the [101] direction, which are held together by hydrogen bonding and O-Ca-O bonds. The structure of the dehydrated compound contains intersecting channels where the calcium atoms are located. The framework consists of corner-sharing VO6 octahedra, PO4 tetrahedra, and P2O7 groups. The connectivity formula is infinity 3Ca2[V(PO4)2/2(P2O7)1/3(P2O7)2/3].